1. Field of the Invention
This invention relates to the field of devices and methods to assist in running or "fishing" a line through a conduit, for example for pulling a cable through an electrical conduit. A pneumatic plug attached to a light line is forced through the conduit and then the line is used to pull through the cable or the like. The invention provides a connector means for removably bridging across the ends of two conduits which terminate at a junction box, such that the plug can be guided serially through two or more conduit sections, instead of fishing through the sections one at a time.
2. Prior Art
In running electrical cabling such as power lines, signal lines, fiber optic cable, etc., a network of hollow conduit sections is mounted to structural members of a building or the like, and the cabling is then pulled into the conduit. The path of particular lines running between terminal points is interrupted by junction boxes at which intermediate connections can be made. After installing the empty conduit along one or more sections, the installer typically pushes a length of material known as a "fish" through a section of uninterrupted conduit from one terminus to the next, the fish being relatively more rigid than the cable so that the fish can be pushed along readily and caused to pass through changes in direction and similar obstructions. The cable is typically more flexible than the fish, and would bend over at obstructions, while the fish does not. The installer attaches an end of the cable to the emerging end of the fish, and then pulls the cable through the conduit back to the insertion end, the cable being fed for example from a spool.
In lieu of a relatively rigid fish, it is known to provide an air blower for forcing through the conduit a plug attached to a string. Means are needed at the blower end of the conduit to pump air into the conduit while allowing the string to pay out as the plug advances with the flow of air. When the plug emerges, the installer affixes an end of the cable to the string and pulls the cable back to the insertion end of the conduit in the same manner as with a fish. Some examples of variations in the nature and use of pneumatic devices for this purpose are disclosed in the following patents, the disclosures of which are hereby incorporated:
U.S. Pat. No. 2,515,953 - Dufresne PA0 U.S. Pat. No. 3,301,531 - Corsiglia PA0 U.S. Pat. No. 3,689,031 - Ruddick et al PA0 U.S. Pat. No. 4,030,702 - Ware et al PA0 U.S. Pat. No. 4,498,659 - Brockelsby, III PA0 U.S. Pat. No. 4,596,381 - Hamrick PA0 U.S. Pat. No. 4,756,510 - Klamm et al PA0 U.S. Pat. No. 4,840,352 - Ellis
Whereas the air blower provides a pressure differential and flow of air through the conduit, the plug is pushed along from the higher pressure blower end of the conduit to a lower pressure emerging end. The process can be expedited by placing a suction device at the emerging end, provided the plug is caught when it emerges. Devices of this kind can quickly string a line through quite a long conduit.
In the case of conduits which define angular variations, such as right angle bends, the pneumatic plug can still pass readily. In pulling a relatively stiff cable back through the conduit, however, it is still difficult at times to draw the end of the cable through such bends. This problem is compounded where two or more bends are involved because of frictional engagement between the cable and the conduit walls at each bend. U.S. Pat. Nos. 4,909,481, 5,029,817 and Des. 318,784, all to Tamm, disclose devices with pulleys intended to assist the passage of a cable around a right angle bend. These devices are not suitable for uninterrupted conduits because they are intended for installation at an openable elbow structure similar to a junction box. These pulley devices are unsuitable for use with a pneumatic plug because they preclude a smooth path for guiding the plug through the elbow, and also open the conduit for escape of air.
A conventional conduit system includes uninterrupted sections of conduit, having smooth inside walls, running between junction boxes having a substantially larger inside area. Although the terminal points of each section are described herein as junction boxes, they could also involve other structures where access to the cable is needed, for example for making terminations, or for installing a supplemental apparatus as in Tamm. The ends of each uninterrupted length of conduit therefore may be coupled to junction boxes, to electrical devices or fittings, or to successive lengths of conduit, "uninterrupted" referring generally to routes of substantially constant inside diameter for passing a pneumatic plug, between two points having a larger inside dimension such as junction boxes, at which the cable can be terminated, coupled to branching cables, etc.
To fish or blow the cable, the installer requires access to both ends of a particular length of conduit. In many applications, the route of a cable will pass through a plurality of junction boxes, electrical devices, branches and the like; however, each of the junction boxes defines a discontinuity. Due to the increase in internal dimensions at the junction box, it is not possible to blow the pneumatic plug through the junction box. In a factory application, for example, the route of a power cable may extend along the ceiling, from end to end of a large building, with a plurality of junction boxes located along the route at regular spacing. At each of the junction boxes, connections are made to conduits with cables leading outwardly or downwardly, to outlets or to fixtures such as light fixtures. This is of course only one example of the many layouts which might be used. The example illustrates a shortcoming with respect to known conduit and cable installation techniques. The installer must repeatedly visit each of the junction box locations in order to complete the installation of the conduit and cable connections at the junction box. Typically the installer repeatedly climbs a ladder, performs a step of the process at one junction box location, moves on to the next location, returns to the previous location, and so on. It will be appreciated that a lot of time is spent in moving and climbing upon the ladder. Similar problems, although possibly less severe, characterize running a cable conduit along a wall, in a floor, etc., due to the need to perform successive operations at each box location.
The successive operations typically include attaching each of the boxes along the route to a secure structure, before or after cutting, bending, attaching together or otherwise forming a length of conduit tubing which reaches to the next or previous box remote from a given location; coupling the conduit at both ends via fittings; fishing or blowing a line from that location to the remote location; attaching a cable to the line at the remote location; pulling the cable into the conduit at the given location; and returning after all the cables to the given box have been run, in order to make the electrical connections. Whereas each box must be visited repeatedly, a great deal of time and effort are required in moving about and climbing the ladder, in addition to the work of actually pulling cables and making connections.
It would be advantageous to arrange a technique for installing conduit and pulling cables which somehow minimizes the need to repeatedly visit individual junction boxes or the like along the route of a cable. However, a means to cut down on accesses is not readily apparent. The conduit-to-junction box connections must be made before the cable can be run. The junction boxes must be visited individually thereafter so that the ends of the conduit lengths which terminate there can be accessed. Two accesses are needed, one for inserting or capturing a fish or plug line which is fed through the respective conduit passage, and a second for attaching or receiving a cable end when the fish or plug line is withdrawn. For these and other reasons here has been no ready solution to the problem to date.